[mythtv-users] mythtv hardware plans

Rod Smith mythtv at rodsbooks.com
Sat Feb 3 17:55:32 UTC 2007

On Saturday 03 February 2007 11:32, jason maxwell wrote:
> So I'd like to get some input.
> I'm working on gathering the hardware to build myself one myth box to
> rule them all. I want to do this right, but cant totally break the
> bank doing it. I'll tell you what the plan is, let me know what you
> think.
> I will have a Comcast coax directly to the mythtv box, no set top box
> at all. I would like to have the option of watching and time shifting
> live or recorded HD content, while also recording other possibly HD
> content simultaneously.
> Here's what I have in mind so far:
> - non-VIA chipset ATX mobo
>   how fast will my proc need to be to do what i want?

The consensus seems to be that you need at least a 3GHz Intel (or equivalent 
AMD) for HD playback; however, there's some variability depending on your 
video card and drivers and the options you set in MythTV. If you want to do 
anything else while playing back HD content, you should go for a dual-core 
and/or or significantly faster CPU. I'd also recommend going at least 
somewhat faster just to provide some buffer in case you find you need to set 
CPU-intensive playback options or if your system is slower than anticipated 
for some reason. At the very least, get a motherboard that will accept faster 
CPUs than you buy initially; that'll let you upgrade the CPU without swapping 
the motherboard if the CPU proves to be inadequate. Note that recording HD 
content is usually not very CPU-intensive; the board just copies the digital 
data stream directly to disk. OTOH, HD tuner cards often (always?) lack 
hardware MPEG-2 encoding for NTSC broadcasts, so they consume a fair amount 
of CPU time when recording NTSC.

> - (2) pcHDTV-5500 capture cards

I'm not sure about the pcHDTV-5500, but the pcHDTV-3000 is known to be weak at 
QAM (digital cable) performance. Specifically, the board tends to lose signal 
lock because of weak 5v power supplied on many systems and/or because of 
interference from other devices in the system. I've got a pcHDTV-3000 and I 
simply cannot get a clean recording from it when I use a video card based on 
an nVidia MX4000 chipset. Using a card with a SiS 330 (aka SiS Xabre 200) 
chipset improves matters, but not enough to get a reliably clean recording. 
Thus, I'd recommend you look into this matter before buying a pcHDTV card. 
The 5500 might be better than the 3000 in this respect; I've not looked into 
it myself. (Note that I don't currently have an HD TV set, just NTSC; I 
bought the pcHDTV cards as "insurance" when the broadcast flag seemed likely 
to darken our doors.)

> - (2) 256MB DDR2 RAM
>   That should be plenty, right?

For most things, yes. I've got a system with 256MB of RAM, though, and I find 
that my swap use occasionally goes up. I suspect there's a memory leak 
somewhere, since swap use just goes up and up over time. I haven't yet 
tracked this down with more precision, though.

> - digital sound
>   I'd like to be able to play back the 5.1 sound from HD recordings if
> possible. Is quality sound possible with onboard audio, or should I
> plan on a decent PCI card? I think i have an old SBLive card somewhere
> I can use. would that work?

I've had luck getting 5.1 output from my Biostar PT880 Pro-A7C motherboard's 
onboard audio. I had to upgrade to a kernel from the 2.6.17 kernel 
provided with Ubuntu, though, and I had to fiddle with mixer settings. I also 
needed a bracket to bring out the motherboard's SPDIF header:


OTOH, another poster here (Rich West) has been having problems with a similar 
setup using a different motherboard.

On the whole, I'd say that 5.1 output in Linux is "bleeding edge" for most 
hardware. I'd recommend first trying any hardware you already own with 
appropriate external connectors, be that your motherboard or a separate sound 
card. If that doesn't work, and if you've got an SPDIF header but no external 
outputs on your motherboard and/or a separate sound card, buy a bracket and 
try it. If THAT doesn't work, then buy another sound card.

Rod Smith

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